WASHINGTON — Democrats on the Senate Commerce Committee sharply criticized the nomination of Jim Bridenstine as NASA administrator in a confirmation hearing Nov. 1, arguing he was not qualified for the job.

Sen. Bill Nelson (D-Fla.), ranking member of the committee, said in an extended opening statement at the hearing that Bridenstine lacked the technical background needed for someone to effectively run NASA, and that his political record suggested he was too divisive to lead the agency.

"While your time as a pilot and your service to our country in the military is certainly commendable, it doesn't make you qualified to make the complex and nuanced engineering, safety and budgetary decisions for which the head of NASA must be accountable," Nelson said. [Presidential Visions for Space Exploration: From Ike to Trump]

Nelson said he feared that having someone in charge with a partisan, rather than technical, background could put at risk the safety of human space transportation systems under development. "Failure at this particular juncture could jeopardize the lives of brave astronauts," he said. "The NASA administrator should be a consummate space professional who is technically and scientifically competent and is a skilled executive."

Bridenstine, in his opening statement, emphasized safety. "Of course, the most important part of any human spaceflight mission is making sure our astronauts return home safely," he said, citing his own experience as a pilot in the U.S. Navy. "I will work to promote a NASA culture where safety, transparency and independent oversight are celebrated."

During the hearing, which lasted more than two and a half hours and focused almost entirely on Bridenstine over three other non-NASA nominees also under consideration, Democratic senators raised questions about Bridenstine's views on Earth science, social issues, and even his tenure as executive director of the Tulsa Air and Space Museum before he was elected to Congress in 2012.

Some senators pressed Bridenstine on his views about the role human activities play in climate change. Sen. Brian Schatz (D-Hawaii) asked Bridenstine if he agreed with the statement that "climate warming trends over the past century are extremely likely due to human activities." Bridenstine responded with "yes."

Bridenstine was reticent, though, to agree with questions by Schatz and other senators about whether human activity was the primary cause of climate change. "Human activity absolutely is a contributor to the climate change that we are currently seeing," he said. Asked by Schatz if it was the primary cause, he said, "It's going to depend on a lot of factors, and we're still learning more about that every day."

Later in the hearing, Sen. Ed Markey (D-Mass.) asked Bridenstine to pledge to protect NASA scientists from any political interference in their Earth science research. "I know, because I've been told by scientists, that fear is rampant among our government scientists that they are going to be punished if they speak publicly about their work on climate change science," Markey said.

"I will not punish them," Bridenstine responded. "I'm not going to reassign anybody basd on that, because that would be punishment."

Several asked him about past statements he made unrelated to NASA, ranging from questions on sexual harassment and LGBTQ rights to criticisms Bridenstine had levied at other Republicans during political campaigns. Some of those issues came up in an Oct. 26 letter by Sen. Patty Murray (D-Wash.), who is not a member of the committee, to committee leadership.

"These are some of the most divisive tactics that this senator has ever seen in either party," Nelson said after describing Bridenstine's support for, among others, a candidate who challenged Sen. John McCain (R-Ariz.) for the Republican nomination in his latest Senate race. "How do you move past all of that and keep NASA from being dragged down?"

Bridenstine emphasized his past work with members of both parties in Congress, including Nelson, on past legislation such as NASA authorization bills. "I want to make sure that NASA remains, as you said, apolitical," he said.

The committee's Republican majority rallied to Bridenstine's defense. "The ranking Democrat on the committee has suggested that you are somehow unqualified to serve as the administrator of NASA because you've taken a number of positions that he deems controversial," said Sen. Mike Lee (R-Utah). "I consider wildly inappropriate this suggestion that this somehow disqualifies you."

Sen. Cory Gardner (R-Colo.) said that he thought the hearing's line of questions was "a little bit disgusting" at times. Gardner was one of the few senators of either party to pose a question on NASA programs outside of Earth science, asking Bridenstine about if he supported continued development of the Orion spacecraft. "Yes sir, 100 percent," Bridenstine responded. [Orion Explained: NASA's Multi-Purpose Crew Vehicle (Infographic)]

There was no sign that the hearing changed any minds among senators about Bridenstine's ability to serve as NASA administrator, with Democratic members of the committee skeptical, if not opposed, to him. "I truly do not think you are ready to be administrator," said Sen. Tammy Duckworth (D-Ill.) at the conclusion of a line of questioning with him.

"This senator is quite skeptical," Nelson said in his opening remarks. "Respectfully, Congressman Bridenstine, I think you've got a long way to go to prove to me you're that leader."

Committee Chairman Sen. John Thune (R-S.D.) said in an interview after the hearing that the committee planned to meet again Nov. 8 to consider these and other nominations. Whether Bridenstine's nomination is included in that hearing, he said, will depend on how quickly members get responses to questions submitted for the record.

Thune criticized Democrats for asking questions on topics he considered not relevant to NASA. "I'd like to hear a little bit more about his views on the space program, his vision for the agency," he said.

If the committee does advance the nomination, action by the full Senate to confirm Bridenstine will depend on other Senate activities as well as "how cooperative the Democrats want to be" regarding the nomination, Thune said. "I think, in the end, the votes will be there, so it's just a question of how long they want to drag it out."

The prospect of a party-line vote on Bridenstine's nomination, at the committee level or by the full Senate, concerned Sen. Ted Cruz (R-Texas), a supporter of Bridenstine. Cruz warned that a partisan vote could hurt bipartisan cooperation on other space policy issues.

"I believe you're going to get confirmed," Cruz told Bridenstine. "But, I would say to my Democratic friends on this committee, that if the confirmation ends up going down to a party-line vote, I think that would be deeply unfortunate for NASA and for the space community."